Origin and Habitat: Originally native to North America, it can now be found worldwide [except on Antarctica] and usually occurs floating just under the surface in stagnant and slow-moving waters (such as lakes, ponds, quiet streams and ditches) that are frequently rich in nutrients or minerals. It can vary widely depending upon its habitat conditions.

Ideal position in aquarium

It is a submerged, free-floating aquatic plant; if planted in the substrate, the lower stem will rot and the plant will become free-floating. It is a true aquatic and will not grow emersed. Excellent floating as a cover for fry. Does well in outdoor ponds.

Lighting requirements

Low to moderate. In lower light growth will be somewhat thin and bright green; in brighter light growth will be even faster and the plant will be bushier and a darker green, becoming yellow or reddish in high light.

Hornwort is a stem plant but one that always floats and never grows roots. The stems may be grouped together and anchored to form a background plant, but portions of the stem buried in the substrate will die and the plant stems will float unless weighed down. Stems can reach a length of more than one metre (3.3 feet). The plant may form rhizoids that are not true roots but do serve to anchor the stem.

The rapid growth of this plant will deter algae, and some sources indicate this plant will also combat algae alleopathically by releasing chemicals that inhibit the growth of algae. Useful in new tanks because of its rapid assimilation of ammonia/ammonium and nutrients. Chemical additives will usually cause the plant to decay.

Flowers may be formed occasionally; fruit is rare. Propagation is chiefly by division of the stems, each of which will form a new plant that may be branched.

This plant was described in 1753 by Carl Linnaeus [often seen as Carl von Linne], the Swedish botanist, zoologist and physician whose catalogue of all then-known species has developed into the binomial nomenclature biological classification system in use today. The genus name derives from the Greek keras [= horn] and phyllon [= leaf]. The species epithet is Latin for submerged. The common name hornwort derives from the "horn" part of the genus name and the Anglo-Saxon "wort" which means plant. Wilmot-Dear (1985) lists four varieties of C. demersum.

Ceratophyllum is the only genus in the Ceratophyllaceae family. The Plant List includes 45 named species, of which only four are valid. Paleobotanical evidence supports a hypothesis that the Ceratophyllaceae are a vestige of ancient angiosperms [flowering plants] that diverged early from the line leading to most other modern taxa. Some authors favour a close relationship of the family to the genus Cabomba of the Nymphaeales. (Les, 1988).